A modal analysis-based RF shimming strategy for parallel transmission in ultra-high-field MRI

This study proposes a modal analysis-based RF shimming strategy that projects multi-channel B1+field distributions onto a dominant modal subspace, enabling low-dimensional modelling and efficient optimization of excitation weights. By leveraging the spatial orthogonality and energy compaction of the modal basis, the method reduces computational complexity while enhancing stability. Simulation and experimental results demonstrate that, compared with conventional RF shimming approaches, the proposed technique achieves superior B1+field uniformity, particularly in anatomically complex regions such as the heart. This provides an effective and robust solution to RF field inhomogeneity caused by shortened wavelengths and dielectric effects in ultra-high field cardiac MRI, thereby improving imaging performance under challenging conditions.